------------------------------------------------------------------------
  h2dp.tex  ApJ letters, 2007, in press
From: "Javier R. Goicoechea" <javier.rodriguez-goicoechea@lra.ens.fr>
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astro-ph/0701559

\documentclass{emulateapj}
\usepackage[latin1]{inputenc}
\usepackage[english]{babel}

\newcommand{\ptsla}{Philos. Trans. R. Soc. London A.}
\newcommand{\sci}{Science}
\newcommand{\tap}{IEEE Trans. Antennas Propagation}
\renewcommand{\jqsrt}{J. Quant. Spec. Radiat. Transf.}

\begin{document}

\title{Far-Infrared detection of H$_2$D$^+$ toward SgrB2\altaffilmark{1}

Departamento de Astrof\'{\i}sica Molecular e Infrarroja, Instituto
de Estructura de la Materia, CSIC, C/ Serrano 121, 28006, Madrid
(Spain)
}
\and
\author{E. Polehampton}

\affil{Space Science \& Technology Department, Rutherford Appleton
Laboratory, Chilton, Didcot, Oxfordshire, OX11 0QX, UK}

\and
\author{J.R. Goicoechea}

\affil{LERMA-LRA, UMR 811, CNRS, Observatoire de Paris et \'Ecole Normale
Sup\'erieure,
24 rue Lhomond, 75231 Paris Cedex 05, France}

\altaffiltext{1}{Based on observations with ISO,
an ESA project with instruments funded by ESA Member States
(especially the PI countries: France, Germany, the Netherlands
and the United Kingdom) and with participation of ISAS and NASA.}

\begin{abstract}
We repport on the first far--IR detection of H$_2$D$^+$,
using the  \textit{Infrared Space Observatory},
in the line of sight toward Sgr~B2  in the galactic center.
The transition connecting the ground level of o-H$_2$D$^+$, 1$_{1,1}$, with
the the 2$_{1,2}$ level at 113 K is observed in absorption against the
continuum emission of the cold dust of the source. The line is broad,
with a total absorption covering 350 km s$^{-1}$, i.e., similar to that
observed in the fundamental transitions of H$_2$O, OH and
CH at $\sim$179, 119 and 149 $\mu$m respectively. For the
physical conditions of the different absorbing clouds
the  H$_2$D$^+$ column density ranges from 2 to 5$\times$10$^{13}$
cm$^{-2}$, i.e.,
near an order of magnitude below
the upper limits obtained from ground based submillimeter telescopes.
The derived H$_2$D$^+$ abundance is of a few 10$^{-10}$,
which agrees
with chemical models predictions for a gas at a kinetic temperature of
$\simeq$20~K.
\end{abstract}